This invention relates to a method and apparatus for injecting fuel into an internal combustion engine. More particularly, this invention relates to a method and apparatus for injecting fuel pulses of variable quantity directly into a combustion chamber of a high speed, compression-ignition diesel engine in timed relation to the rotational position of the engine crankshaft.
A number of conventional fuel injection systems have been used to inject fuel into internal combustion engines. However, conventional fuel injection systems suffer from a number of recognized deficiencies, especially when applied to high speed engines.
One of these recognized deficiencies is the functional complexity of conventional fuel injection systems which require the precise cooperation of many component parts. Further, many of the component parts are themselves structurally and functionally complex. Such multi-layered complexity adds to the manufacturing, assembly and maintenance time and costs of conventional fuel injection systems as well as increasing the probability of malfunction.
Another recognized deficiency of conventional fuel injection systems comes to light when an attempt is made to apply these systems to a diesel engine capable of high speed operation. Because the cyclic time of a high speed engine is very short, one or more of the component parts of conventional fuel injection systems are unable to function properly at the high cyclic rate. Consequently, conventional fuel injection systems are unable to properly supply fuel to a high speed engine so that the engine fails to fully attain its potential for speed and power output.
One symptom of this shortcoming is that diesel engines have traditionally been thought of as comparatively low-speed, low specific-horsepower engines best suited for stationary use or for heavy-duty vehicular use. Thus, until recently, the spark ignition engine has been the preferred engine for automotive use. However, recognition of the inherent thermodynamic superiority of the diesel engine has led to its application to automotive vehicles. Further, the need for light weight, fuel efficient vehicles has led to the development of comparatively small-displacement, high specific-horsepower output diesel engines employing supercharging or turbocharging to enable the diesel engine to produce horsepower somewhat comparable to a spark-ignition engine. However, such engines have been unable to attain their full speed potential because of the deficiencies of conventional fuel injection systems.
One of the limiting deficiencies of conventional fuel injection systems becomes vexingly apparent at high engine speeds. Because conventional fuel injection systems typically use a plunger to pressurize a selected quantity of fuel in a measuring chamber from a comparatively low pressure to an injection pressure opening a valve to begin injection, the compressibility of the fuel imposes an inherent delay between stroking of the plunger and the beginning of injection. At low engine speeds delays caused by compressibility of the fuel do not pose an insurmountable obstacle to successful use of conventional fuel injection systems. However, as engine speed increases the flexibility of system components along with inertia and momentum effects combine with the compressibility of the fuel so that the selected quantity of fuel cannot be raised to injection pressure and injected into a combustion chamber of the engine in the time available. Experience has shown that in conventional fuel injection systems the liquid fuel has an apparent compressibility of about 0.5 percent per 1000 psi. of pressure applied to the fuel. About 0.15 percent is attributable to elastic deformation of component parts of the fuel injection system with the remainder representing actual compression of the liquid fuel. Thus, it can be seen that a considerable amount of "slack" must be removed from a conventional fuel injection system before each injection pulse can begin. For example, if the pressure of the measured quantity of fuel is increased by 10,000 psi. to reach injection pressure, it will decrease in apparent volume by about 5 percent before reaching injection pressure. Thus, the fuel injection system must provide an additional 5 percent of plunger movement to take up the "slack" in the system and provision must be made to allow for the timing of the injection pulse to compensate for the concommittant delay caused by compression of the fuel.
A further manifestation of fuel compressibility arises in those conventional fuel injection systems having the plunger located some considerable distance from the injection nozzle. When the injection nozzle valve closes at the end of an injection pulse, a pressure wave is created in the fuel trapped behind the nozzle. This pressure wave travels through a conduit to the plunger where it is reflected back to the injection nozzle. Upon arriving at the injection nozzle, the pressure wave may have sufficient amplitude to momentarily unseat the nozzle valve so that fuel dribbles into the combustion chamber at an undesirable time. Such fuel dribbling adversely effects the exhaust emissions of the engine as well as decreasing its fuel efficiency.
Another aspect of high speed diesel engines is that they are generally of comparatively small displacement with small pistons and cylinders so that space around the combustion chamber in the head of these engines is very limited. Thus, in order to deliver an appropriate quantity of fuel to a combustion chamber in the time available while using a necessarily small injector nozzle, comparatively high injection pressures must be used. For example, injection pressures of about 20,000 psi. are employed in some conventional fuel injection systems. Of course, increased injection pressures cause increased compression of the fuel and exacerbate the deficiencies outlined above.
U.S. Pat. Nos. 3,465,737; 3,859,973; 3,908,621; 3,913,548; 3,936,232; 3,951,117; 3,968,779; 3,983,855; 4,019,835; 4,050,433; 4,138,981 and 4,149,506 illustrate examples of conventional fuel injection systems.
In view of the deficiencies of conventional fuel injection systems it is a primary object for this invention to provide a fuel injection apparatus and method for a high speed diesel engine.
Another object for this invention is to provide a fuel injection apparatus and method which is comparatively simple in structure and function.
Another object for this invention is to provide a fuel injection method and apparatus which avoids the limitations imposed on conventional fuel injection systems by the compressibility of liquid fuels.
Still another object is to provide a fuel injection method and apparatus which does not rely upon the pressurization of a measured quantity of fuel to open an injection nozzle to begin injection of a fuel pulse into an engine.
Another object for this invention is to provide a fuel injection apparatus and method wherein an injection nozzle is opened by creating a fluid pressure differential across a plunger member movable to open the nozzle.
Still another object for this invention is to provide a fuel injection apparatus and method which does not rely upon a pressure increase of a measured quantity of fuel to deliver the measured quantity of fuel through an injection nozzle to a combustion chamber.
Another object for this invention is to provide a fuel injection method and apparatus wherein a quantity of pressurized fuel at a determined pressure level is measured and delivered through an injection nozzle to a combustion chamber substantially at the determined pressure level.
Yet another object for this invention is to provide a fuel injection apparatus and method wherein a plunger is moved by pressurized fluid at a determined pressure level to deliver a measured quantity of fuel to a combustion chamber.
These and other objects and advantages of this invention will be apparent in light of the following detailed description of two preferred embodiments of the invention.